Countdown doesn't show when added to img tag

The countdown shows when pasting the url into a browser but not when its in an img tag. Any ideas why?

[https://pageone.marketing/countdown-timer/countdown.php?time=2019-12-25+00:00:01]

`<img src="https://pageone.marketing/countdown-timer/countdown.php?time=2019-12-25+00:00:01">`